Passive control of high-speed separated flows using splitter plates

An experimental investigation was conducted to study the effects of passive splitter plates placed in the recirculation region behind a blunt-based axisymmetric body aligned in supersonic flow (Mach 2.49). The goals of this research were to obtain a better understanding of the physical phenomena that govern these massively separated high-speed flows and to determine the flow-control authority of these passive devices. Triangular splitter plates dividing the near wake into one-half-, one-third-, and one-fourth-cylindrical regions were designed to exploit specific stability characteristics of this flow, to affect the near-wake flow, to alter the base pressure, and to ultimately affect base drag. Mean and high-frequency static-pressure measurements were acquired on the base to assess the influence of these plates. Schlieren imaging, surface flow visualization, and pressure-sensitive paint measurements were also employed to document the near-wake flowfield, surface flow structure, and surface pressure, respectively. The timeaveraged base pressure distribution, time-series pressure fluctuations, and presumably the stability characteristics were altered by the spatial division of the near wake. The area-integrated pressure was only slightly affected. Normalized root-mean-square levels indicate pressure fluctuations were significantly reduced (as much as 39%) with the addition of the splitter plates. Power-spectral-density estimates revealed a spectral broadening of fluctuating energy for the one-half-cylinder configuration and a bimodal distribution for the one-third- and one-fourth-cylinder configurations.